Oxidized LDL through LOX-1 modulates LDL-receptor expression in human coronary artery endothelial cells

Experimental studies have shown that oxidized low-density lipoprotein (ox-LDL) up-regulates its receptor LOX-1. Both ox-LDL and LOX-1 are expressed in atherosclerotic plaques. Native LDL concentrations are elevated in atherosclerosis, suggesting a reduction in LDL-receptors. We hypothesized that ox-LDL via LOX-1 could influence the expression of LDL-receptors. This study was designed to examine the interaction between ox-LDL, LOX-1, and LDL-receptors in human coronary artery endothelial cells (HCAECs). HCAECs were incubated with ox-LDL (10-80 microg/ml) for 3-24h. Ox-LDL decreased the expression of LDL-receptor in a concentration- and time-dependent fashion. The effects of ox-LDL were mediated by its endothelial receptor LOX-1, since pretreatment of HCAECs with a blocking antibody to LOX-1 (JTX92, 10 microg/ml) prevented the effect of ox-LDL on LDL-receptor expression. The role of LOX-1 was further confirmed by the use of an antisense to LOX-1 mRNA, which also blocked the effect of ox-LDL in LDL-receptor expression. In other experiments, ox-LDL as expected induced superoxide anion generation; and pretreatment of HCAECs with the anti-oxidants trolox and alpha-tocopherol (each 10 microM) inhibited the formation of superoxide anions as well as the down-regulation of LDL-receptor in response to ox-LDL. These studies provide the first evidence that ox-LDL via LOX-1 modulates LDL-receptor expression in HCAECs. The generation of free radicals elicited by ox-LDL may be a key step in this process.     

cDNA microarray analysis of altered gene expression in Ara-C-treated leukemia cells

The acute lymphoblastic leukemia cell line CCRF-CEM is sensitive to Ara-C and undergoes apoptosis. In contrast, the chronic myelogenous leukemia (CML) cell line K562 is highly resistant to Ara-C, which causes the cells to differentiate into erythrocytes before undergoing apoptosis. We used cDNA microarrays to monitor the alterations in gene expression in these two cell lines under conditions leading to apoptosis or differentiation. Ara-C-treated CCRF-CEM cells were characterized by a cluster of down-regulated chaperone genes, whereas Ara-C-treated K562 cells were characterized by a cluster of up-regulated hemoglobin genes. In K562 cells, Ara-C treatment induced significant down-regulation of the asparagine synthetase gene, which is involved in resistance to L-asparaginase. Sequential treatment with Ara-C and L-asparaginase had a synergistic effect on the inhibition of K562 cell growth, and combination therapy with these two anticancer agents may prove effective in the treatment of CML, which cannot be cured by either drug alone.     

Degradation of the D1 protein of photosystem II under illumination in vivo: two different pathways involving cleavage or intermolecular cross-linking

The D1 protein of the photosystem II reaction center turns over the most rapidly of all the proteins of the thylakoid membrane under illumination in vivo. In vitro, the D1 protein sustained cleavage in a surface-exposed loop (DE loop) or cross-linking with another reaction center protein, the D2 protein or cytochrome b(559), under illumination. We found that the D1 protein was damaged in essentially the same way in vivo, although the resultant fragments and cross-linked adducts barely accumulated due to digestion by proteases. In vitro studies detected a novel stromal protease(s) that digested the adducts but not the monomeric D1 protein. These observations suggest that, in addition to cleavage, the cross-linking reactions themselves are processes involved in complete degradation of the D1 protein in vivo. Peptide mapping experiments located the cross-linking sites with the D2 protein among residues 226-244, which includes the cross-linking site with cytochrome b(559) [Barbato, R., et al. (1995) J. Biol. Chem. 270, 24032-24037], in the N-terminal part of the DE loop, while N-terminal amino acid sequencing of the fragment located the cleavage site around residue 260 in the C-terminal part of the loop. We propose a model explaining the occurrence of simultaneous cleavage and cross-linking and discuss the mechanisms of complete degradation of the D1 protein in vivo.     

Enhanced chemiluminescence of 6-(4-methoxyphenyl)imidazo[1,2-a]pyrazin-3(7H)-one by attachment of a cyclomaltooligosaccharide (cyclodextrin). Attachment of cyclomaltononaose (delta-cyclodextrin)

2-Methyl-6-(4-methoxyphenyl)imidazo[1,2-a]pyrazin-3(7H)-one (MCLA) is an oxygen-induced chemiluminescent compound. It has been shown that the chemiluminescence can be enhanced by forming a cyclomaltooligosaccharide (cyclodextrin)-bound MCLA, and therefore, in continuation of the survey of the types of cyclodextrins, in this study, MCLA was attached to the secondary hydroxyl face of delta-cyclodextrin, which consists of nine D-glucose units. Although the oxygen-induced chemiluminescence efficiency of delta-cyclodextrin-bound MCLA in a pH 8.0 aqueous phosphate buffer was 12 times greater than that of MCLA, the efficiency was markedly lower than that of gamma-cyclodextrin-bound MCLA, which exhibited the highest chemiluminescence efficiency in the previous investigation. Although fluorescence efficiency and light-emitter formation efficiency for delta-cyclodextrin-bound MCLA were similar to those for gamma-cyclodextrin-bound MCLA, singlet-excited state formation efficiency for delta-cyclodextrin-bound MCLA was lower than that for gamma-cyclodextrin-bound MCLA. This study distinctly indicated the optimum cyclodextrin for construction of greatly luminescent cyclodextrin-bound MCLA is gamma-cyclodextrin.     

Gene silencing in chick embryos with a vector-based small interfering RNA system

In this paper, the use of vector-based RNA interference (RNAi) to specifically interfere with gene expression in chick embryos is reported. In ovo electroporation was carried out to transfer a small interfering RNA (siRNA) expression vector into chick embryos. En2 was chosen for the target gene because the family gene, En1, is expressed in a similar pattern. Four sets of 19-mer sequences were designed with the En2 open reading frame region connected to a sequence of short hairpin RNA (shRNA), which exerts siRNA effects after being transcribed, and inserted into pSilencer U6-1.0 vector. En2 and En1 expression were suppressed by the siRNA whose sequence completely matched En2 and En1. Suppression occurred when the siRNA sequence differed by up to two nucleotides from the target sequence. The sequence that differed by four nucleotides from the target gene did not show siRNA effects. One set that completely matched the En2 target did not show siRNA effects, which may be due to location of the siRNA in the target gene. Thus, multiple sets of shRNA must be prepared if we are to consider. This system will greatly contribute to the analysis of function of genes of interest, because the target gene can be silenced in a locally and temporally desired manner.     

Ceriporic acid C, a hexadecenylitaconate produced by a lignin-degrading fungus, Ceriporiopsis subvermispora

A lignin-degrading basidiomycete, Ceriporiopsis subvermispora produces a series of alkyl- and alkenylitaconates (ceriporic acids). Previously, two alkylitaconic acids with tetradecyl and hexadecyl side chains were isolated and identified as 1-heptadecene-2,3-dicarboxylic acid (ceriporic acid A) and 1-nonadecene-2,3-dicarboxylic acid (ceriporic acid B). In the present study, one hexadecenylitaconate (ceriporic acid C) was isolated and its chemical structure was analyzed by glycolation and subsequent (1) trimethylsilation, or (2) acetalation with acetone and acetone-d6. Analyses of the isolated metabolite demonstrated that the hexadecenylitaconic acid was (Z)-1,10-nonadecadiene-2,3-dicarboxylic acid. The structure of the side chain in ceriporic acid C was the same as that of hexadecenylcitraconate, chaetomellic acid B. Thus, it was found that ceriporic acids share close structural similarity with alk(en)yl citraconate derivatives, chaetomellic acids and other lichen lactones, protolichesterinic, lichesterinic, and murolic acids.     

Reduction of phosphodiesterase 3B gene expression in peroxisome proliferator-activated receptor gamma (+/-) mice independent of adipocyte size

Phosphodiesterase 3B (PDE3B) gene expression is generally reduced in large adipocytes of obese, insulin-resistant mice. This reduced gene expression is restored by peroxisome proliferator-activated receptor (PPAR) gamma ligands accompanied by a reduced fat cell size. To determine whether PDE3B gene expression is regulated by PPAR gamma itself, we analyzed lean PPAR gamma (+/-) mice with adipocyte size comparable to control PPAR gamma (+/+) mice. In adipocytes of PPAR gamma (+/-) mice, PDE3B mRNA and protein were both reduced to 63% of wild-type levels. Basal PDE activity tended to be decreased to 70% of wild-type levels, and, similarly, insulin-induced PDE activity was significantly decreased to 70%. Thus, PPAR gamma is required for PDE3B gene expression independent of adipocyte size.     

Type III Cu mutants of Myrothecium verrucaria bilirubin oxidase

Type III Cu ligand, His456 and His458, of Myrothecium verrucaria (MT-1) bilirubin oxidases (BO) [EC 1.3.3.5] were doubly mutated as to Lys, Asp, and Val. In spite of perturbation of the type III Cu centers, these mutants were pale blue or colourless when isolated. However, they became intense blue on reaction with reducing agents such as dithionite, ascorbate, hexacyanoferrate(II), and octacyanotangstate(IV) under air, or with an oxidizing agent such as hexacyanoferrate(III), indicating that they are in mixed forms when expressed in Aspergillus oryzae. His456.458Lys and His456.458Asp mutated as to potential coordinating groups showed weak BO and ferroxidase activities, while His 456.458Val mutated as to non-coordinating groups showed no enzyme activity at all.     

Cross-talk between the pathways leading to the induction of apoptosis and the secretion of tumor necrosis factor-alpha in ricin-treated RAW 264.7 cells

Ricin induced apoptotic nuclear morphological changes in mouse macrophage cell line RAW264.7 cells at concentrations sufficient to cause severe protein synthesis inhibition. Ricin also induced the release of tumor necrosis factor-alpha (TNF-alpha) from this cell line in a dose-dependent manner but the profile was bell-shaped. However, the isolated galactose-specific ricin B-chain had no such effects. These results suggest that the receptor-binding of ricin through the B-chain is not enough, and subsequent attack on the intracellular target, i.e., the 28S ribosomal RNA (rRNA), by the A-chain of internalized ricin is required for the effects of ricin. Z-D-CH2-DCB, a caspase family inhibitor, showed potent inhibition of the release of TNF-alpha from RAW264.7 cells as well as blockage of the induction of apoptosis by ricin. Furthermore, SB202190, a specific P38 mitogen-activated protein (MAP) kinase inhibitor that strongly inhibits the release of TNF-alpha, also showed significant inhibition of ricin-induced apoptosis. These results suggest that there may be cross-talk between the pathways leading to the release of TNF-alpha and apoptosis. Time course analysis revealed that the activation of p38 MAP kinase started prior to the induction of TNF-alpha release and apoptosis. Since the activation of p38 MAP kinase in ricin-treated RAW264.7 cells was not prevented by Z-D-CH2-DCB, the activation of p38 MAP kinase may occur upstream of the caspase cascade. Among the other protein synthesis inhibitors examined, modeccin and anisomycin, which can trigger a ribotoxic stress response similar to ricin, induced the release of TNF-alpha, but emetine and cycloheximide did not. These results suggest that the specific attack on the 28S ribosomal RNA and the resulting ribotoxic stress response may trigger the multiple signal transduction pathways through the activation of p38 MAP kinase, which in turn leads to TNF-alpha release and apoptosis.